Definition of anemia ro bbins
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anemia
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Robbins pathology definition anemia hemoglobin hematocrit
Anemia is a reduction in the oxygen-carrying capacity of blood due to a decrease in the total circulating red cell mass. In practice, it is identified by a reduced hemoglobin concentration and usually a reduced hematocrit for the person's age and sex.
Robbins classifies anemia mechanistically into:
- Diminished erythropoiesis - inadequate red-cell production
- Blood loss
- Increased red-cell destruction (hemolysis)
Source: Robbins, Cotran & Kumar Pathologic Basis of Disease, section “Anemias of Diminished Erythropoiesis,” p. 591.
Hemoglobin conc in Robbins
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anemia definition hemoglobin
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Robbins Pathologic Basis of Disease anemia defined hemoglobin concentration hematocrit
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In Robbins, anemia is diagnosed when the hemoglobin concentration is below the normal range for age and sex.
Typical adult hemoglobin reference values given in Robbins are:
- Male: approximately 13.5-17.5 g/dL
- Female: approximately 12.0-16.0 g/dL
Thus, a practical definition is Hb <13.5 g/dL in men and <12 g/dL in women.
Robbins, Cotran & Kumar Pathologic Basis of Disease, Anemias chapter.
If we take haemoglobin conc as measure of anaemia but why we take red cell mass
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anemia hemoglobin concentration versus red cell mass plasma volume definition
Because anemia is fundamentally a decrease in total oxygen-carrying red-cell/hemoglobin mass, not merely a low laboratory concentration.
But in practice we measure hemoglobin concentration because it is simple, rapid, and usually correlates well with red-cell mass.
The difference
- Red-cell mass = the total quantity of circulating RBCs in the body.
- Hemoglobin concentration = hemoglobin per unit volume of blood, for example g/dL.
[
\text{Hb concentration} = \frac{\text{total hemoglobin mass}}{\text{blood volume, especially plasma volume}}
]
Therefore, Hb concentration is affected by both:
- Total RBC/hemoglobin mass
- Plasma volume
Why red-cell mass matters
A low Hb concentration can occur even when actual red-cell mass is normal, if plasma volume is expanded.
Example: pregnancy
- Plasma volume increases more than red-cell mass.
- Hb and hematocrit fall by dilution.
- This is called physiologic anemia of pregnancy.
Conversely, with dehydration:
- Plasma volume falls.
- Hb concentration and hematocrit may appear normal or high.
- Yet the patient may actually have reduced red-cell mass.
Key point
- For definition/pathophysiology: anemia means decreased red-cell mass or total hemoglobin mass, causing reduced oxygen-carrying capacity.
- For routine diagnosis: we use Hb concentration, because direct measurement of red-cell mass requires specialized methods, historically radiolabeled RBC techniques, and is not routinely practical.
Also, in acute hemorrhage, immediately after blood loss, both RBCs and plasma are lost proportionately. Hb concentration may initially remain normal even though total red-cell mass has fallen. It decreases later after plasma refill or IV fluids cause hemodilution.
Robbins, Cotran & Kumar Pathologic Basis of Disease, Anemias chapter. A laboratory text similarly emphasizes that hematocrit reflects the concentration of red cells, not total red-cell mass.
What is red cell mass
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red cell mass hematocrit plasma volume
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red cell mass definition total volume circulating erythrocytes plasma volume
Red-cell mass (RCM) means the total volume or total amount of circulating red blood cells in the body.
It is not the same as the RBC count, hematocrit, or hemoglobin concentration measured in one blood sample.
[
\text{Total blood volume} = \text{plasma volume} + \text{red-cell mass}
]
Simple example
Suppose two people have the same total amount of RBCs:
- Person A has normal plasma volume: Hb concentration is normal.
- Person B has excess plasma volume, such as in pregnancy: the same RBCs are diluted, so Hb concentration and hematocrit are lower.
Thus, Person B may have a low Hb concentration without a true reduction in total red-cell mass.
Relationship to hematocrit
- Red-cell mass: total RBC volume in the entire circulation, usually expressed as mL or mL/kg.
- Hematocrit: percentage of a blood sample occupied by RBCs.
[
\text{Hematocrit} = \frac{\text{red-cell volume}}{\text{total blood volume}} \times 100
]
Hematocrit is therefore a concentration value and changes when plasma volume changes.
According to Robbins: anemia is a reduction of total circulating red-cell mass below normal limits, leading to reduced oxygen-carrying capacity. In clinical practice, hemoglobin concentration is used as its convenient surrogate.
Robbins, Cotran & Kumar Pathologic Basis of Disease, Anemias, p. 591.
Robbins, Cotran & Kumar Pathologic Basis of Disease, Anemias, p. 591.
Rbc indices value in Robbins
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erythrocyte indices MCV MCH MCHC
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MCV MCH MCHC normal values hematology reference ranges
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RBC indices: Adult reference values in Robbins
| Index | Meaning | Men | Women |
|---|---|---|---|
| MCV | Mean corpuscular volume, average RBC size | 78-98 fL | 78-98 fL |
| MCH | Mean corpuscular hemoglobin, average Hb amount per RBC | 26-34 pg | 26-34 pg |
| MCHC | Mean corpuscular hemoglobin concentration, Hb concentration in packed RBCs | 32-36 g/dL | 31-36 g/dL |
| RDW | Red-cell distribution width, variation in RBC size | 11.8-14.5% | 12.2-16.1% |
Associated values in the same Robbins table:
| Parameter | Men | Women |
|---|---|---|
| Hemoglobin | 13.2-16.6 g/dL | 11.6-15.0 g/dL |
| Hematocrit | 38-49% | 35-45% |
| RBC count | 4.4-5.6 × 10⁶/µL | 3.9-5.1 × 10⁶/µL |
| Reticulocyte count | 0.6-2.7% | 0.6-2.7% |
Interpretation
- Low MCV: microcytic anemia
- Normal MCV: normocytic anemia
- High MCV: macrocytic anemia
- High RDW: anisocytosis, meaning increased variation in RBC size
Robbins & Kumar Basic Pathology, Table 10.2, “Adult Reference Ranges for Red Blood Cells,” p. 383.
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